Block copolymer hot melt adhesive composition

ABSTRACT

Hot melt adhesive compositions comprising a block copolymer, aluminum powder, glass fiber and hollow inorganic silicate microspheres. The block copolymer is selected from the group consisting of copolyesters, copolyamides, copoly(esteramides) and copoly(ether-esters) melting at a temperature above about 150° C. and having from about 30 to about 70 weight percent of hard segments and from about 70 to about 30 weight percent of soft segments. The weight ratio of block copolymer to aluminum powder, glass fiber and silicate microspheres is in the range of about 3:7 to about 3:2, the weight ratio of block copolymer to glass fiber is at least about 2:1, the weight ratio of glass fiber to aluminum powder is at least about 1:9 and wherein the volume percent of silicate microspheres is less than about 10. The compositions are particularly useful for filling voids and cavities in substrates.

The present invention relates to a hot melt adhesive composition, to amethod of filling voids with the adhesive composition and to articlesfilled or coated with the hot melt adhesive composition. Moreparticularly, it relates to block copolymers containing glass fibers,aluminum powder and hollow inorganic silicate microspheres, to a methodof filling voids with such compositions and to articles, filled orcoated with the compositions.

Hot melt adhesives are well known in the prior art. These materials areconveniently applied to a substrate in the molten state and upon coolingform an adhesive bond. However, a deficiency common to most of the hotmelt adhesives of the prior art is their tendency to soften and flow atelevated temperatures, as, for example, 70° to 100° C. with a resultingloss of bond strength. Consequently, these materials are not suitablefor use over a broad temperature range.

Attempts to upgrade the softening and flow temperatures have involvedusing very high molecular weight resinous materials and/or crosslinkingof the resin. These methods have resulted in materials with highersoftening points and flow temperatures. However, in most cases theresulting material was not adapted to thermal processing because itshigher molecular weight and/or crosslinked structure engenderedextremely high application viscosity. Thus, these materials were notsuitable for use as hot melt adhesives.

In the manufacture and repair of metal bodies of automobiles andappliances, solder compositions containing lead are frequently used tofill cavities and voids. These lead solders are extremely dense and canadd a significant increment to the weight of the metal body. Theypresent a health hazard which mandates special handling to protectworkers engaged in the soldering and cavity filling operations. Curableadhesives such as epoxies are generally unsatisfactory for such cavityand void filling applications because they require careful metering ofthe components to provide good physical properties and bond strength,because they take too long to cure to a sandable state and because theyhave rather poor weather resistance. Conventional hot melt adhesives arealso unsatisfactory for cavity and void filling applications becausethey cannot be sanded rapidly at assembly line speed, they do notreadily accept paint, exhibiting "telegraphing" or "bleed-through", andthey do not withstand the high temperatures necessary for the subsequentcure of paint overcoats. "Telegraphing" or "bleed-through" are termsused to describe the revelation of difference in composition of thesubstrate when it has been painted, because of a difference inreflectivity between the painted metal and the painted adhesivecomposition.

U.S. Pat. No. 3,650,999 discloses block copolymer comprising hardpolyester segments and soft polyamide segments having improved adhesionand high temperature performance obtained by reacting a crystallinepolyester, a C₁₈ to C₅₄ polycarboxylic acid and a primary diamine. Thispoly(esteramide) in common with other hot melt adhesives hasdeficiencies in creep resistance at temperatures above 150° C. in therange up to 205° C. and above and in shrinkage when the hot melt iscooled to room temperature after application. These deficiencies havebeen overcome to a considerable degree by incorporating a metal powderinto the block copolymer to yield a cavity filling composition whichpossesses good sandability and paint acceptance. However, the metalpowder copolymer composition can lack adequate impact resistanceespecially at low temperatures and can sag excessively at elevatedtemperatures. Attempts to improve the impact resistance by introducingan energy-absorbing reinforcement were generally unsuccessful and addeda further complication of blinding of the sanding disc, making sandingextremely difficult.

The present invention is directed to an adhesive composition of improvedimpact resistance at low temperatures, which is less dense and toxicthen lead solder, forms a strong bond to metal and painted metalsubstrates, withstands extremes of humidity and temperature, has sagresistance at elevated temperatures, is readily trowelled to fill acavity, sets rapidly to a sandable state, is easily sanded smooth andaccepts paint without "bleed-through".

The adhesive composition comprises a block copolymer, aluminum powder,glass fiber and hollow inorganic silicate microspheres; wherein theblock copolymer is selected from the group consisting of copolyesters,copolyamides, copoly(esteramides) and copoly(ether-esters) melting at atemperature of at least about 150° C., having from about 30 to about 70weight percent of hard segments and from about 70 to about 30 weightpercent of soft segments, wherein the weight ratio of block copolymer toaluminum powder, glass fiber and silicate microspheres is in the rangeof about 3:7 to about 3:2, wherein the weight ratio of block copolymerto glass fiber is at least about 2:1, wherein the weight ratio of glassfiber to aluminum powder is at least about 1:9 and wherein the volumepercentage of silicate microspheres is less than about 10.

Another aspect of the invention is directed to substrates coated orfilled with the adhesive composition and yet another aspect is directedto a method of filling a cavity in a substrate which comprises applyingthe adhesive composition as a hot melt to fill the cavity, cooling theadhesive composition below the crystallization temperature of the blockcopolymer and sanding the adhesive composition to provide a surface evenwith the surrounding substrate.

The block copolymer of the adhesive compositions of the presentinvention is selected from the group consisting of copolyesters,copolyamides, copoly(ester-amides) and copoly(ether-esters) melting at atemperature of at least about 150° C., having hard segments and softsegments to provide a balance of physical properties and processability.These are considered to exist in microscopic domains within the bulkmass of copolymer resin to provide a heterophase system in which thecopolymer will have physical properties reflecting the properties whichthe respective segments would manifest independently. By control of therelative size, proportions, crystallinity and crystal melting points ofthe segments, the tack, open time and bond strength of the adhesive canbe controlled. The hard segments contribute crystalline blocks to thecopolymer so that optimum bulk physical properties such as tensilestrength and stiffness can be achieved without incurring thedisadvantage of high processing viscosity.

The hard or crystalline segments can be polyester or polyamide of weightaverage molecular weight of from about 400 to about 16,000 to ensurethat the segment will contribute the optimum ordered structure to thefinal polymeric product. Polyesters and polyamides with a weight averagemolecular weight of less than about 400 have a short chain length andcannot contribute the necessary ordered structure to the final polymericproduct which also comprises soft segments. Polyesters and polyamideswith a weight average molecular weight of greater than about 16,000 mayrequire excessive reaction times or temperatures to form the final blockcopolymer leading to degradation of the polymer and a subsequent loss inadhesive properties. To ensure that the final polymeric product hasexcellent thermal properties such as resistance to flow at elevatedtemperatures the melting point of the hard polyester or polyamidesegment should be at least about 180° C. Preferably, the melting pointis in the range of from 200° C. to 270° C.

The hard or crystalline polyester segments of the block copolymer arecondensed from at least one aliphatic or alicyclic diol having from 2 to10 carbon atoms and at least one alicyclic or aromatic dicarboxylic acidhaving from 8 to 20 carbon atoms selected to give a melting point in thedesired range. Representative examples of such acids are terephthalicacid, isophthalic acid, hexahydroterephthalic acid, the naphthalicacids, such as 2,6-, 2,7-, 2,8-, 1,4- and 1,5-naphthalene dicarboxylicacids and other such acids which form high melting polyester resins.Examples of glycols are ethylene glycol, propylene glycol,tetramethylene glycol, neopentylene glycol, 1,4-cyclohexane diol,1,4-cyclohexane dimethanol and other such glycols. High melting polymerscontaining components such as 2,2-dimethylpropane diol, form polyesterswhich have melting points above 234° C. Mixtures of the foregoingpolyesters can also be used.

Preferably, a polyester from the following group can be used to providethe hard segments of the block copolymer:

Poly(ethylene terephthalate/isophthalate), 100/0 to 75/25;

Poly(ethylene/hexamethylene terephthalate), 100/0 to 75/25;

Poly(ethylene/neopentylene terephthalate), 100/0 to 75/25;

Poly(tetramethylene terephthalate/isophthalate), 100/0 to 75/25;

Poly(tetramethylene/hexamethylene terephthalate), 100/0 to 75/25;

Poly(tetramethylene/neopentylene terephthalate), 100/0 to 75/25;

Poly(ethylene/propylene terephthalate), 100/0 to 60/40; and

Poly(tetramethylene 2,6-naphthalate/terephthalate), 100/0 to 75/25; etc.

When the hard polyester segments comprise polyethylene terephthalate,the molecular weight range corresponds to an inherent viscosity range ofabout 0.05 to about 0.7 dl/g⁻¹ determined at 25° C. with a solution of0.5 g/100 ml in a solvent pair consisting of phenol andsym-tetrachloroethane in the weight ratio of 60:40.

The hard or crystalline polyamide segments of the block copolymer can becondensed from at least one aliphatic or alicyclic diamine having from 2to 12 carbon atoms and at least one aliphatic or alicyclic dicarboxylicacid having from 2 to 12 carbon atoms selected to provide a polyamidewith a melting point in the desired range. Examples of diamines includeethylene diamine, 1,3-propane diamine, 1,4-butanediamine, 1,5-pentanediamine, hexamethylene diamine 1,10-decanediamine, cyclohexanediamine,etc. Examples of acids include oxalic, malonic, succinic, glutaric,adipic, pimelic, suberic, azelaic, and sebacic acids. The hard orcrystalline polyamide segments of the block copolymer can be obtained bypolymerization of ω-aminocarboxylic acids containing from 2 to 10 carbonatoms such as aminoacetic acid, 3-aminopropionic acid, 4-aminobutyricacid, 6-aminohexoic acid, 10-aminodecanoic acid, etc. Polymerization oflactams such as ε-caprolactam provides a route to several of suchpolyamides. Among the preferred polyamides are poly(hexamethyleneadipamide) and poly(ε-caprolactam).

The soft, amorphous or low melting segments of the block copolymercontribute wettability, elasticity and rubber character to thecopolymer. They can be polyester, poly(ether-ester) or polyamide and aregenerally of weight average molecular weight in the range of about 300to about 16,000 and possess a glass transition temperature less thanabout 50° C. and more preferably in the range of about -30° to about 40°C.

The soft polyester segments of the block copolymer can be condensed froman aliphatic or alicyclic diol having from 4 to 10 carbon atoms and analiphatic, alicyclic or aromatic dicarboxylic acid having from 4 to 54carbon atoms selected to provide a polyester with a glass transitiontemperature in the desired range. They can be formed by reacting apolylactone diol of number average molecular weight in the range ofabout 350 to 6000 with an aliphatic, alicyclic or aromatic dicarboxylicacid having from 4 to 54 carbon atoms. Poly(ether-ester) segments can beprepared by condensing a poly(alkylene ether) glycol of number averagemolecular weight in the range of about 350 to 6000 in which the alkylenegroups have from 2 to 10 carbon atoms with an aliphatic, alicyclic orarmoatic dicarboxylic acid having from 4 to 54 carbon atoms. Polyamidesegments can be prepared by condensing an aliphatic or alicyclic diaminehaving from 2 to 12 carbon atoms with a mixture of an aliphatic oralicyclic dicarboxylic acid having from 4 to 54 carbon atoms and atleast 40 weight percent of an aliphatic dicarboxylic acid having from 18to 54 carbon atoms.

The block copolymers are prepared by a one step or two step method. Inthe one step method the components which form the hard or soft segmentsare polymerized in the presence of a prepolymer of the soft or hardsegments respectively. In the two step method the hard segments and softsegments are prepared separately as prepolymers and then condensedtogether.

The preferred block copolymer component of the present inventioncontains about 30 to about 70 percent by weight of hard segments andconversely about 70 to about 30 percent by weight of soft segments. Itis further characterized as having a weight average molecular weight inthe range of about 5500 to about 30,000, more preferably in the range ofabout 8000 to about 20,000 for an optimal balance of physical propertiesand processability. The melting point of the copolymer component isabove about 150° C. and is preferably in the temperature range of about155° to about 225° C. for ease of processing without degradation of thecopolymer. The glass transition temperature associated with the softsegments of the copolymer is generally less than about 50° C. and ispreferably in the range of about -30° to 40° C. to contributewettability, elasticity, and rubber character to the copolymer. Themelting point and glass transition temperature are convenientlydetermined with a duPont differential thermal analyzer Model DTA 900with the scanning calorimeter attachment, employing a 5 to 25 mg sampleheated at a rate of 20° C. per minute, in a nitrogen atmosphere. Themelt viscosity of the copolymer determined at 232° C. is preferably lessthan 150,000 centipoise at a shear rate of 4 sec.⁻¹ and is preferably inthe range of about 25,000 to 100,000 centipoise.

The most preferred group of block copolymers are blockcopoly(ester-amides) of the type described in U.S. Pat. No. 3,650,999.They comprise hard segments of polyester as described hereinabove, andsoft segments of polyamide formed by condensing a C₁₈ to C₅₄dicarboxylic acid and a C₂ to C₁₀ aliphatic or alicyclic primarydiamine. The dicarboxylic acids include the "dimer acids" obtained bydimerization of unsaturated aliphatic monocarboxylic acids, e.g.,linoleic acid, available commercially as mixtures of monobasic, dibasicand tribasic acids. The aliphatic or alicyclic diamines include ethylenediamine, 1,3-propane diamine, 1,4-butanediamine, 1,5-pentane diamine,hexamethylene diamine, 1,10-decanediamine, cyclohexanediamine,2,2-dimethyl-1,3-propane diamine, etc.

Optionally up to 60 percent by weight of a linear aliphatic dibasic acidhaving from 4 to 17 carbon atoms may be substituted for thecorresponding amount of the C₁₈ to C₅₄ polycarboxylic acid used toprepare the soft polyamide segments of the polyesteramide. Examples ofthese acids include oxalic, succinic, adipic, pimelic, suberic, azelaic,sebacic, dodecanedioic and thapsic acids. The advantage of substitutingthe C₄ to C₁₇ acids for the C₁₈ to C₅₄ acids is to provide a moreheterogeneous character to the polyamide segments of the polymer and tomodify the glass transition temperature.

The second component of the adhesive composition is a finely dividedaluminum powder added to improve the creep resistance of the blockcopolymer and the sandability. It may be of average particle size in therange of about 0.2 micron to about 150 microns and is preferably ofaverage particle size in the range of about 4 to about 50 microns. It ispreferred to use an atomized aluminum of generally spheroidal shapeparticularly when the adhesive composition is used for cavity fillingsince it allows the hot melt composition to be readily smoothed andburnished when it is sanded. In general, plate-like, acicular ormulti-faceted granular aluminum powders are unsatisfactory, surprisinglycausing high viscosity in the hot melt and "blinding" or filling andocclusion of sand paper when the adhesive composition is sanded.

In addition to improving the creep resistance and sandability of theadhesive composition, the aluminum powder improves the rate of meltingof the adhesive composition, allows the composition to be applied andspread or trowelled more easily with less pressure, allows longerworking time or longer "open" time between application of the hot meltand closing of the bond and higher "green" strength or faster onset ofbond strength, and reduces the degree of shrinkage of the adhesivecomposition when it is cooled from the hot melt temperature to ambienttemperature.

When the adhesive composition comprises only the block copolymer and thealuminum powder, the impact resistance tends to be low particularly atlow temperatures such as -30° C. and the molten composition tends to sagat the elevated temperatures at which it is applied. Addition of glassfiber as the third component of the adhesive composition improves theimpact resistance at low temperatures, reduces the tendency of theadhesive composition to sag at elevated temperatures and permits greaterlatitude in overcoming shrinkage and minimizing coefficient of expansiondifferences with the substrate. The glass fiber is of the typeconventionally used for reinforcement of thermoplastic resins. It ispreferred to use relatively soda-free glasses comprising lime-aluminumborosilicate glass such as types "C" and "E" glass. The glass fibershould preferably be in the form of milled fibers or chopped fibers ofaverage length in the range of about 1/32 inch (0.8 mm) to about 2/3inch (6.4 mm) and longer and of diameter in the range of about 2 toabout 20 microns. The preferred average length is in the range of about1/16 inch (1.6 mm) to about 1/4 inch (6.4 mm).

The introduction of glass fiber into the adhesive composition comprisingblock copolymer and aluminum powder can cause an undesirable decrease inthe flow and workability particularly at higher weight ratios of theseinorganic components and can require such higher temperatures forapplication and smoothing of the composition that decomposition of theblock copolymer may tend to occur. The addition of a minor amount ofinorganic silicate microspheres can cause a further increase in meltviscosity and hence sag resistance but surprisingly the pressurerequired to extrude the adhesive composition is not appreciably affectedand the flow and workability of the hot melt extrudate are not impairedand indeed in the preferred compositions are actually improved.Consequently, a sufficient amount of inorganic silicate microspheres isincluded in the adhesive composition to obtain this increase in meltviscosity but the amount is limited so that the flow and workability arenot impaired. Generally up to about 10 volume percent and preferablyfrom about 2 to about 8 volume percent of the total composition isrequired. The silicate microspheres are hollow synthetic inorganicsilicate microspheres of average particle size in the range of about 10to about 150 microns, and preferably in the range of about 50 to about100 microns. Their average effective particle density is in the range ofabout 100 g per liter to about 400 g per liter and is preferably in therange of about 150 g per liter to about 250 g per liter. Suchmicrospheres are sold for example by the Philadelphia Quartz Companyunder the registered trademark Q-Cel. Because of the low density of thesilicate microspheres, they comprise less than 2.5 weight percent of theadhesive composition, and preferably less than 1.5 weight percentdepending upon the effective particle density of the microspheres. Incontrast to the effect obtained with the hollow microspheres, when anequivalent volume of solid microspheres is added to the adhesivecomposition significant increases in melt viscosity and the pressurerequired to extrude the melt are observed and the flow and workabilityof the hot melt composition is impaired.

The inorganic components of the adhesive composition may optionally betreated with an effective amount of coupling agent by methods well knownto those skilled in the art before or while being blended into the blockcopolymer. Such coupling agents include organosilane coupling agentsexemplified by triethoxy vinyl silane, vinyl methyl dichlorosilane,2-(trimethoxysilyl)ethyl methacrylate, 3-amino-1-triethoxysilylpropane,etc.; organotitanium coupling agents such as the alkyl alkanoyltitanates exemplified by C₁ to C₄₀ alkyl stearyl titanates; fatty acidsexemplified by oleic and stearic acid, fatty amides exemplified bymethacrylato chromic chloride. These coupling agents can cause asignificant reduction in the melt viscosity of the blend, can improvethe wetting and dispersion of the inorganic components (i.e. thealuminum powder and the glass fiber) and can enhance the physicalproperties of the adhesive composition.

The ratio of the components of the adhesive composition is selected sothat the desired balance of flow and workability, adhesion, sagresistance, impact resistance and sandability is achieved. Excessiveamounts of glass fiber and silicate microspheres should be avoided sincethey contribute to very high melt viscosity, cause poor workability asmanifested by the difficulty with which the composition can be spread ortrowelled and feathered onto a substrate, and decrease the adhesion ofthe adhesive composition to the substrate. It is therefore, preferred toselect the components so that the weight ratio of block copolymer toinorganic components, i.e., to the sum of aluminum powder, glass fiberand inorganic silicate microspheres, is in the range of about 3:7 toabout 3:2 and is preferably in the range of about 1:2 to about 1:1; theweight ratio of block copolymer to glass fiber is at least about 2:1 andis preferably in the range of about 2:1 to about 10:1; the weight ratioof glass fiber to aluminum powder is at least about 1:9 and ispreferably in the range of about 1:4 to about 1:1; and the inorganicsilicate microspheres comprise up to about 10 volume percent of theadhesive composition. The component ratios are preferably selected sothat the melt viscosity of the hot melt composition is less than about600,000 centipoise and preferably less than about 300,000 centipoise ata temperature of 250° C. and a shear rate of 4 sec⁻¹ measured in aBrookfield Thermocel Unit Model HBT. When the melt viscosity is greaterthan 600,000 centipoise, the hot melt is difficult to apply and spread,and tends to be dragged from the point of application.

The hot melt composition is formed by mixing the aluminum powder, theglass fiber and the hollow inorganic silicate microspheres with themelted polymer in any convenient way such as by melt blending in ablender-extruder. A good mix is considered to have been obtained if thefiller particles are evenly distributed throughout the melt. In poormixes, the filler particles are not adequately wet by the melt, and tendto be unevenly distributed remaining aggregated within the melt. Meltstability of the mix is determined by maintaining the mix at 216° C. fortwo hours. If the melt viscosity changes less than ±10 percent duringthis time, the mix is considered to have melt stability.

Creep resistance of the compositions of the present invention isdetermined by observing the sag of a 10 to 15 gram sample of thecomposition placed on an aluminum plane inclined at 60° to the vertical.The observations are carried out at 175° and 205° C. Creep or sag inless than 60 minutes at the designated temperature is recorded as afailure to meet the test.

Impact strength is determined by applying the composition as a hot meltat 500° F. (260° C.) to a smooth steel panel 7.5 cm×22.5 cm to provide astrip 4 cm wide and in the range of 25 to 250 microns thick. The panelsare conditioned for 24 hours at -30° C. One lb. (454 g) steel balls aredropped onto the strip of composition from heights of 18 inch (46 cm)and 36 inch (92 cm). The impact is repeated three times at 15 minuteintervals. If chipping or cracking of the composition or separation fromthe steel panel occurs, the composition is considered to have failed thetest.

Similar test panels are prepared for testing of the sandability of thecomposition. In the preparation of the panels, the pressure needed toextrude the hot melt composition at 260° C. through a 3/16 (4.76 mm)nozzle is noted, and the ease of flow of the hot melt extrudate and itsability to be worked by spreading, trowelling and feathering it to asmooth cohesive strip is observed. The panel is cooled to roomtemperature and a disc sander, 12.5 cm. diameter, with 80 grit mediumtungsten carbide abrasive, is applied to the composition at 1000 rpm tofurther smooth and feather the composition. If the surface of thecomposition becomes smooth enough to accept paint without "telegraphing"or showing a difference in reflectivity between the painted steel andthe painted composition, and without blinding or blocking the abrasivesurface of the sander, the composition is rated sandable.

Depending upon the particular substrate and especially when thesubstrate is bare metal, it can be advantageous to apply a primer coatto improve the adhesion of the hot melt composition. Suitable primersinclude the commercially available primer coatings, and the etherifiedmethylolmelamines described in U.S. Pat. No. 4,053,682. Also suitable,can be organic solvent solutions and aqueous dispersions of the blockcopolymer component of the hot melt adhesive composition.

The hot melt adhesive compositions of the present invention findwidespread utility in a wide variety of applications. They areespecially valuable in those applications where resistance to creep atelevated temperatures is a necessary requirement. The adhesivecompositions of the present invention may be used to great advantage tobond a variety of substrates including metal, glass, synthetic andnatural textiles, leathers, synthetic polymeric sheet material, wood,paper, etc.

The present invention also includes the concept of incorporating variousingredients into the adhesive composition to improve processing and/orperformance of these materials. These additives and adjuncts includeantioxidants, thermal stabilizers, extenders, dyes, pigments, adhesionpromoters, plasticizers, etc.

The following examples are set forth in illustration of the inventionand should not be construed as a limitation thereof. Unless otherwiseindicated, all parts and percentages are by weight.

EXAMPLE 1

A block copolymer which is approximately 65 percent by weightcrystalline polyethylene terephthalate segements and 35 percent byweight amorphous polyamide made from dimer acid and hexamethylenediamine is prepared in two steps. In the first step 157.5 parts (0.272mol) of a C₃₆ dibasic acid and 30.8 parts (0.266 mol) of hexamethylenediamine are charged to a reaction vessel and heated with agitation atabout 215° C. for one hour to form a polyamide resin. During the first30 minutes the pressure rises to 1000 kPa after which time the reactionvessel is vented to reduce the pressure to 600 kPa. At the end of onehour the pressure is released and 332 parts of a crystallinepolyethylene terephthalate (M.P. -260° C./inherent viscosity 0.147) and7.5 parts (0.095 mol) of ethylene glycol are charged to the vessel alongwith a minor amount of an antioxidant. The vessel is flushed withnitrogen and the mixture is heated to about 280° C. while maintaining anitrogen pressure of 240 kPa. After 0.5 hour the vessel is vented andvacuum applied and the reaction is continued under full vacuum (0.1 to 5mm. of mercury) for two hours. At the end of this time the resultingmolten poly(ester-amide) is discharged under pressure into a water bathto quench the material. The polymer obtained melts at 205° C. and theinherent viscosity is 0.50.

To a stainless steel reactor fitted with an anchor agitator and ajacketed hot oil heating system is added 100 parts by weight of thepoly(ester-amide) and heating is begun. When the contents have reached250° C., agitation is begun at 60 rpm and 200 parts by weight of amixture of 149 parts dry aluminum powder of average particle size about17 microns, sold by the Aluminum Company of America under the tradenameAtomized Powder 123, 49 parts milled glass fiber of average length 1/16inch (1.59 mm), and 1.8 parts hollow inorganic silicate microspheressold by Philadelphia Quartz Company under the registered tradename Q-Cel300, of average particle size 75 microns, is fed into the mass at a rateof 10 parts by weight per minute. The agitation is continued and thetemperature raised to 266° C. under a nitrogen blanket. Agitation iscontinued for 15 minutes after the addition of the mixture is completeand the molten mass is discharged under slight N₂ pressure (250 kPa),quenched in a bath, ground and redried. The melt viscosity of thecomposition at 250° C. is 198×10³ centipoise. The pressure required toextrude the hot melt at 260° C. through an orifice of 3/16 inch diameter(4.76 mm) is 70 psi (482 kPa).

The adhesive composition is used as a hot melt to fill dents andorifices in a metal plate. If flows and is readily trowelled to yield asmooth coherent mass. It is cooled to room temperature, sanded smoothwith 80 grit tungsten carbide abrasive and painted with an automotivesurface coating. No "telegraphing" is observed. The composition passesthe 18 inch pound (2.03 Joule) and the 36 inch pound (4.07 Joule) impacttests.

EXAMPLES 2-11

Hot melt adhesive compositions are prepared by the procedure of Example1 from the block copolymer of Example 1. The weight ratio of blockcopolymer to inorganic components in Examples 2-7 is 1:2 and in Examples8-11 is 2:3. The weight ratio of aluminum powder to glass fiber is 3:1.In Examples 2-4, 10 and 11 hollow inorganic silicate microspheres areincorporated into the adhesive composition. Examples 5 and 8 contain nomicrospheres and Examples 6, 7 and 9, included for comparative purposes,contain solid glass microspheres of average particle size 25 microns.The processability of the hot melt adhesive compositions is evaluated bydetermining the melt viscosity, the pressure required to cause flowthrough a 3/16 inch (4.76 mm) orifice and the ease of flow andworkability of the hot melt composition applied at a temperature of 260°C. The data including results of Example 1 are presented in Table 1.Examples 4, 9 and 11 show the increase in melt viscosity obtained withthe hollow microspheres. Examples 1, 3 and 10 containing hollowmicrospheres in the volume percentage range of about 2 to about 6 showimproved flow and/or workability in comparison with Examples 5 and 8without microspheres. In contrast when the microspheres are solid(Examples 6, 7 and 9) or when the concentration is greater than 10volume percent (Examples 4 and 11) a very significant increase inpressure for melt extrusion accompanies the increase in melt viscosityand the flow and workability of the hot melt composition issubstantially impaired.

The lap bond tensile strength of the adhesive composition of Example 10,determined by ASTM Test Method D-1002-72 is 149 kg cm².

                                      TABLE I                                     __________________________________________________________________________    EFFECT OF MICROSPHERES ON PROCESSABILITY OF HOT MELT COMPOSITIONS                                                 Pressure                                                                Melt  needed                                         Weight Ratio             Viscosity                                                                           for flow                                                                           Flow Workability                          Block Copolymer:                                                                         Weight %                                                                             Volume %                                                                             at 250° C.                                                                   at   at   (applied at                     Example                                                                            Inorganic Compounds                                                                      Microspheres                                                                         Microspheres                                                                         cps × 10.sup.-3                                                               260° C.                                                                     260° C.                                                                     260° C.                  __________________________________________________________________________    1    1:2        0.61 (h)                                                                             5      198   70   good v.good                          2    1:2        0.14 (h)                                                                             1.2    228   75   poor poor                            3    1:2        0.30 (h)                                                                             2.5    208   75   fair fair                            4    1:2        1.5 (h)                                                                              11.7   >4000 100  v.poor                                                                             untrowelable                    5    1:2        0      0      216   70   fair poor                            6    1:2        6.1 (s)                                                                              4.8    452   95   poor v.poor                          7    1:2        30 (s) 10.4   >4000 100  v.poor                                                                             untrowelable                    8    2:3        0      0      120   40   good good                            9    2:3        7.1 (s)                                                                              5.2    200   100  fair poor                            10   2:3        0.78 (h)                                                                             5.9    282   25   excellent                                                                          v.good                          11   2:3        1.38 (h)                                                                             10.1   >4000 100  no flow                                                                            untrowelable                    __________________________________________________________________________     h  hollow, s  solid                                                      

EXAMPLE 12

A block copolyester of inherent viscosity about 0.6 containing 65 weightpercent of polyethylene terephthalate as the hard segments interlinkedby means of terephthaloyl bis-N-butyrolactam with 35 weight percent ofcopoly(hexamethylene isophthalate-terephthalate) (I:T, 80:20), as thesoft segments, is melt blended with the aluminum powder, glass fiber andhollow microspheres of Example 10 and in the weight ratios disclosedtherein. The blending process is effected by the method described inExample 1. The blend is used as a hot melt to fill dents and orifices ina metal plate.

EXAMPLE 13

By the melt blend process of Example 1, a blend of a blockcopoly(ether-ester) of inherent viscosity about 0.6 containing 65 weightpercent of polybutylene terephthalate as the hard segments and 35 weightpercent of the copolyisophthalateterephthalate (I:T, 80:20) ofpolytetramethylene ether glycol (having a number average molecularweight about 600) as the soft segments, is prepared from the aluminumpowder, glass fiber and hollow microspheres described in Example 1, inthe weight ratio of Example 10. The blend is used as a hot melt to filldents and orifices in a metal plate.

EXAMPLE 14

The polyamide of dimer acid and hexamethylene diamine described inExample 1 is melt reacted with a polyhexamethylene adipamide of numberaverage molecular weight about 8000, in the weight ratio of 40:60 toprovide a block copolyamide. The copolyamide is melt blended with thealuminum powder, glass fiber and hollow microspheres described inExample 1 and by the process set forth in Example 1. The weight ratio ofcopolymer, aluminum powder, glass fiber and microspheres is40:44.6:14.6:0.8. The blend is used as a hot melt to fill dents andorifices in a metal plate.

What is claimed is:
 1. An adhesive composition comprising a block copolymer, aluminum powder, glass fiber and hollow inorganic silicate microspheres; wherein the block copolymer is selected from the group consisting of copolyesters, copolyamides, copoly(esteramides) and copoly(ether-esters) melting at a temperature of above about 150° C., having from about 30 to about 70 weight percent of hard segments and from about 70 to about 30 weight percent of soft segments; wherein the weight ratio of block copolymer to aluminum powder, glass fiber and silicate microspheres is in the range of about 3:7 to about 3:2, wherein the weight ratio of block copolymer to glass fiber is at least about 2:1, wherein the weight ratio of glass fiber to aluminum powder is at least about 1:9 and wherein the volume percentage of silicate microspheres is less than about
 10. 2. The adhesive composition of claim 1 wherein the hard segments of the block copolymer are polyester condensates of an aliphatic or alicyclic diol having from 2 to 10 carbon atoms and an alicyclic or aromatic dicarboxylic acid having from 8 to 20 carbon atoms, or polyamide condensates of an aliphatic or alicyclic diamine having from 2 to 12 carbon atoms and an aliphatic or alicyclic dicarboxylic acid having from 2 to 12 carbon atoms, or polyamide condensates of an ω-aminocarboxylic acid having from 2 to 12 carbon atoms; and wherein the soft segments of the block copolymer are polyester condensates of an aliphatic or alicyclic diol having from 4 to 10 carbon atoms or a polylactone diol of molecular weight in the range of about 350 to 6000 and an aliphatic, alicyclic or aromatic dicarboxylic acid having from 4 to 54 carbon atoms, or poly(ether-ester) condensates of a poly(alkylene ether) glycol of molecular weight in the range of about 350 to about 6000 in which the alkylene groups have from 2 to 10 carbon atoms and an aliphatic, alicyclic or aromatic dicarboxylic acid having from 4 to 54 carbon atoms, or polyamide condensates of an aliphatic or alicyclic diamine having from 2 to 12 carbon atoms and a mixture of an aliphatic or alicyclic dicarboxylic acid having from 4 to 54 carbon atoms containing at least 40 weight percent of an aliphatic dicarboxylic acid having from 18 to 54 carbon atoms.
 3. The adhesive composition of claim 1 wherein the block copolymer is a copolyester wherein the hard segments are condensed from an aliphatic or alicyclic diol having from 2 to 10 carbon atoms and an alicyclic or aromatic dicarboxylic acid having from 8 to 20 carbon atoms and the soft segments are condensed from an aliphatic or alicyclic diol having from 4 to 10 carbon atoms or a polylactone diol of molecular weight in the range of about 350 to about 6000 or a poly(alkylene ether) glycol of molecular weight in the range of about 350 to about 6000 in which the alkylene groups have from 2 to 10 carbon atoms and an aliphatic, alicyclic or aromatic dicarboxylic acid having from 6 to 54 carbon atoms.
 4. The adhesive composition of claim 1 wherein the block copolymer is a copolyamide wherein the hard segments are condensed from an aliphatic or alicyclic diamine having from 2 to 12 carbon atoms and an aliphatic or alicyclic dicarboxylic acid having from 2 to 12 carbon atoms or from an ω-aminocarboxylic acid having from 2 to 12 carbon atoms and the soft segments are condensed from an aliphatic or alicyclic diamine having from 2 to 12 carbon atoms and a mixture of aliphatic and alicyclic dicarboxylic acids having from 4 to 54 carbon atoms containing at least 40 weight percent of an aliphatic dicarboxylic acid having from 18 to 54 carbon atoms.
 5. The adhesive composition of claim 1 wherein the block copolymer is a copoly(ester-amide) wherein the hard segments are condensed from an aliphatic or alicyclic diol having from 2 to 10 carbon atoms and an alicyclic or aromatic dicarboxylic acid having from 8 to 20 carbon atoms and the soft segments are condensed from an aliphatic or alicyclic diamine having from 2 to 12 carbon atoms and a mixture of aliphatic or alicyclic dicarboxylic acids having from 4 to 54 carbon atoms containing at least 40 weight percent of an aliphatic dicarboxylic acid having from 18 to 54 carbon atoms.
 6. The adhesive composition of claim 1 wherein the block copolymer is a copoly(ester-amide) wherein the hard segments are condensed from an aliphatic or alicyclic diamine having from 2 to 12 carbon atoms and an aliphatic or alicyclic dicarboxylic acid having from 2 to 12 carbon atoms or from an ω-aminocarboxylic acid having from 2 to 12 carbon atoms and the soft segments are condensed from an aliphatic or alicyclic diol having from 4 to 10 carbon atoms or a poly(alkylene ether) glycol of molecular weight in the range of about 350 to about 6000 in which the alkylene groups have from 2 to 10 carbon atoms and an aliphatic, alicyclic or aromatic dicarboxylic acid having from 6 to 54 carbon atoms.
 7. The adhesive composition of claim 5 wherein the polyester is selected from the group consisting of poly(ethylene terephthalate), poly(tetramethylene terephthalate), co-poly(butylene terephthalate)-(ethylene terephthalate), co-poly(ethylene terephthalate)-(ethylene isophthalate) and copoly(ethylene terephthalate)-(propylene terephthalate) and wherein the polyamide segments are condensed from a C₃₆ dimer acid and hexamethylene diamine.
 8. The adhesive composition of claim 1 having a melt viscosity at 250° C. of less than about 600,000 centipoise at a shear rate of 4 sec.⁻¹.
 9. The adhesive composition of claim 1, 5 or 6, wherein the hard segment prior to incorporation in the block copolymer has a weight average molecular weight in the range of about 400 to about 16,000 and a melting point in the range of about 180° to about 270° C.
 10. The adhesive composition of claim 9 wherein the block copolymer has a weight average molecular weight in the range of about 5500 to about 30,000 and a glass transition temperature in the range of about -30° to 40° C.
 11. The adhesive composition of claim 10 wherein the aluminum powder is spheroidal and has an average particle size in the range of about 0.2 to about 150 microns.
 12. The adhesive composition of claim 10 wherein the aluminum powder is spheroidal and has an average particle size in the range of about 4 to about 50 microns.
 13. The adhesive composition of claim 11 wherein the glass fiber is milled glass fiber of average length at least about 0.8 mm.
 14. The adhesive composition of claim 12 wherein the glass fiber is milled glass fiber of average length at least about 0.8 mm.
 15. The adhesive composition of claim 13 wherein the silicate microspheres comprise from about 2 to about 8 volume percent of the adhesive composition and are of average particle size in the range of about 10 to about 150 microns.
 16. The adhesive composition of claim 14 wherein the silicate microspheres comprise from about 2 to about 8 volume percent of the adhesive composition and are of average particle size in the range of about 50 to about 100 microns.
 17. An adhesive composition comprising:(a) a poly(ester-amide) block copolymer of weight average molecular weight in the range of about 5500 to about 30,000 and of melting point in the range of about 155° C. to about 225° C., having from about 30 to 70 percent by weight of crystalline polyester segments selected from the group consisting of poly(ethylene terephthalate), poly(tetramethylene terephthalate), co-poly(butylene terephthalate)-(ethylene terephthalate), co-poly(ethylene terephthalate)-(ethylene isophthalate) and co-poly(ethylene terephthalate)(propylene terephthalate) which prior to incorporation in the poly(ester-amide), have a weight average molecular weight in the range of about 400 to about 16,000 and a melting point in the range of about 180° to about 270° C., and from about 70 to about 30 percent by weight of amorphous polyamide segments of glass transition temperature in the range of about -30° to 40° C., condensed from a C₁₈ to C₅₄ dibasic acid and an aliphatic or alicyclic diamine containing from 2 to 10 carbon atoms; (b) spheroidal aluminum powder of average particle size in the range of about 4 to about 50 microns; (c) milled glass fiber of average length in the range of about 1.6 mm to about 6.4 mm; and (d) hollow inorganic silicate microspheres of average particle size in the range of about 10 to about 150 microns;wherein the weight ratio of block copolymer to aluminum powder, glass fiber and silicate microspheres is in the range of about 1:2 to about 1:1, wherein the weight ratio of block copolymer to glass fiber is in the range of about 2:1 to about 10:1, wherein the weight ratio of glass fiber to aluminum powder is in the range of about 1:4 to about 1:1, and wherein the silicate microspheres comprise from about 2 to about 8 volume percent of the adhesive composition.
 18. The adhesive composition of claim 17 wherein the dibasic acid is a C₃₆ dimer acid and the diamine is hexamethylene diamine.
 19. The adhesive composition of claim 18 wherein the crystalline polyester segments are poly(ethylene terephthalate).
 20. The adhesive composition of claim 17 having a melt viscosity at 250° C. of less than about 600,000 centipoise at a shear rate of 4 sec.⁻¹.
 21. A substrate coated with the composition of claims 17, 18 or
 19. 22. A substrate in which there is a cavity filled with the composition of claims 17, 18 or
 19. 23. A substrate coated with the composition of claim
 10. 24. A substrate coated with the composition of claim
 15. 25. A substrate coated with the composition of claim
 16. 26. A substrate in which there is a cavity filled with the composition of claim
 10. 27. A substrate in which there is a cavity filled with the composition of claim
 15. 28. A substrate in which there is a cavity filled with the composition of claim
 16. 